1. Field of the Invention
The present invention relates to hard disk drives, and a method for managing scratches on hard disk drives
This application claims priority under 35 U.S.C. §119 from Korean Patent Application No. 10-2005-0130803, filed on 27 Dec. 2005, the disclosure of which is hereby incorporated by reference herein as if set forth in its entirety.
2. Description of Related Art
Hard disk drives (HDDs) are memory devices used to record and reproduce data by converting digital electronic pulses to tiny magnetic structures placed on a ferromagnetic medium. Since the HDD can access a large amount of data at high speed, it is widely used as an auxiliary memory device for computer systems.
Unfortunately, a given disk of the HDD itself may develop defects with use, or a defect may inadvertently be generated during manufacture. For example, during manufacture, a defect can be generated on a multilayered media disk due to scratches occurring as a head stack assembly is loaded on the disk. Further, as HDD technology evolves to enable HDDs to rotate at higher rpm speeds and/or the TPI (tracks per inch) and BPI (bits per inch) densities increase, the likelihood of scratches developing in various directions due to a mechanical shock (or other factors) increases. One type of defect highly likely to be generated are scratches running along an oblique line caused by a head that reciprocates while tracing a circular arc on a rotating disk.
Obviously, physical damage, such as scratches, can cause both loss of data and data capacity in a disk. Since the controllable basic unit of a disk in a HDD is a sector, a scratch that intersects any portion of a sector can result in the loss of the entire sector. Thus, it is desirable to minimize any disk damage due to scratches.
Since a sector having any defect is classified as a defective sector, recording or writing of data to the sector is usually prohibited. Thus, in the HDD manufacturing process, disks are scanned for defects, and the address of any sector having a defect is written to a “maintenance zone” on the disk dedicated to maintaining lists of defective sectors. Thus, when a user is accessing the disk, the user can be prevented from accessing a defective sector by first accessing the maintenance zone.
FIG. 1 is a flowchart for explaining the manufacturing process of a general HDD. As shown in FIG. 1, the manufacturing process of an HDD includes a mechanism assembly step 100, a servo write step 110, a function test step 120, a burn-in step 130, a final test step 140, and a shipping test, packaging and shipping step 150.
The purpose of the mechanism assembly step 100 is to assemble a head disk assembly (HDA). The HDA is a mechanical part of the HDD, and the assembly of the HDA is carried out in a clean room. Next, during the servo write step 110, a servo writer is used to write a servo write pattern on the surface of a disk for the servo control of an actuator.
The function test step 120 is a test step performed after coupling the HDA of step 100 and a printed circuit board (PCB) made in a PCB assembly step. The purpose of function test step 120 is to test whether the HDA and the PCB are appropriately coupled and operate normally.
The burn-in step 130 is next performed. The burn-in step requires the longest period of all the manufacturing steps of a HDD. Generally, a burn-in step is performed by a program (firmware) residing in the HDD while the HDD sits on a rack in a burn-in room. The burn-in step 130 allows a user to use the HDD normally by detecting disk defects in advance so as to later avoid using the defective areas.
Next, the “final test” step 140 is used to check whether an HDD that passed the earlier burn-in step 130 has also normally passed a defect processing step. Once the final test step 140 is completed, the HDD passes through the shipping test, packaging, and shipping step 150 where it is shipped as a complete product.
Note that in the burn-in step 130, a “defect detection test” is performed on the surface of a disk. The defect detection test includes a “read/write test”, which is performed over the entire area of the surface of a disk while applying stress to a read/write channel whereby a microprocessor that controls the overall operation of the HDD makes the head of the HDD's actuator drift off track or changes the HDD's read/write channel parameter values.
During the read/write test, sectors having defects can be detected as data written to each sector will be later read and tested for one or more data errors. As mentioned above, the address of the sector containing a defect can be recorded in a special defect list located in a particular area on the disk, that is, in the maintenance zone on the disk. Subsequently, as the defect list can be used to avoid accessing defective sectors, an HDD having effectively defect-free performance is provided.
However, the defect detection test is not perfect—generally due to inaccuracies of the actuator head. Accordingly, a known filtering algorithm (i.e., a “scratch fill” algorithm) can be used to detect patterns of scratches to provide information as to where undetected defects can be expected to exist. Scratch fill algorithms basically look at the defects identified on the media and fill in gaps between closely spaced defects as these typically are indicative of continuous scratches in the media surface. This approach attempts to anticipate where sector defects that are not detected during generation of a defect list are likely to occur and essentially fill in the gaps, as well as pad the identified defects.
Unfortunately, conventional defect detection and predictions technologies do not adequately address spiral scratches running across the surface of a disk or other similar medium. Thus, it is difficult to perform a scratch fill operation for spiral scratches. Therefore, there is a need to effectively expect and manage disk defects due to spiral scratches.